The invention relates to an X-ray diagnostic system for producing radiographs, comprising an x-ray image intensifier and a camera for photographing the X-ray image intensifier-output image as well as comprising an automatic exposure timer which exhibits an integrator for detecting the light quantity per image, and a threshold value switch for disconnecting the X-ray tube upon reaching a desired light quantity.
An X-ray diagnostic system of this type is described in the German AS No. 1 929 894 (U.S. Pat. No. 3,546,461 issued Dec. 8, 1970). This known X-ray diagnostic system serves the purpose of preparation of cine radiographs. For each individual image of a cinematographic series, the X-ray tube is switched off after reaching a predetermined light quantity, so that optimally exposed individual images are obtained.
Upon occurrence of a switch-off signal for termination of an image exposure, the light at the image intensifier output does not immediately disappear, but decays slowly because the high voltage cables are still being discharged via the X-ray tube, and the image intensifier still exhibits somewhat of an afterglow or persistence. However, the light quantity actually acting on the x-ray film thereby exceeds the specified setpoint value. The time constant for the decay behavior is not fixed, but variable; it is dependent upon the radiographic data. Therefore, the decay cannot be compensated by a simple correction circuit; i.e., by reduction of the setpoint value of the light quantity by a predetermined fixed value.